Failover and load balancing

ABSTRACT

Provided are techniques for failover when at least one of a first network adapter and a data path through the first network adapter fails, wherein the first network adapter is connected to a filter driver, and wherein the first network adapter is connected to a second network adapter. With the filter driver, a path fail notification is received that at least one of the first network adapter and the data path through the first network adapter has failed. With the filter driver, packets directed to the first network adapter are rerouted to the second network adapter.

RELATED APPLICATIONS

This application is a National Stage filing under 35 U.S.C. §371 ofInternational Application No. PCT/RU2004/000105, filed on Mar. 19, 2004.

BACKGROUND

1. Field

The disclosure relates to a method, system, and program for failover andload balancing.

2. Description of the Related Art

An I_T nexus is a pairing of an initiator device and a target device.The devices that request input/output (I/O) operations are referred toas initiators and the devices that perform these operations are referredto as targets. For example, a host computer may be an initiator, and astorage device may be a target. The target may include one or moreseparate storage devices.

A Host Bus Adapter (HBA) is a hardware device that “connects” theoperating system and a Small Computer System Interface (SCSI) bus. TheHBA manages the transfer of data between the host computer and thecommunication path. HBA teaming refers to grouping together several HBAsto form a “team,” where each HBA in a team is connected and may routedata to a particular target. HBA teams may be built on an Internet SmallComputer System Interface (iSCSI) (IETF RFC 3347, published February2003) portal group concept. iSCSI has been defined as a standard by IETFFebruary 2003. A portal group concept may be described as a collectionof Network Portals within an iSCSI Network Entity that collectivelysupport the capability of coordinating a session with connectionsspanning these portals.

HBA teaming may be used with Small Computer System Interface (SCSI)(American National Standards Institute (ANSI) SCSI Controller Commands-2(SCC-2) NCITS.318:1998) initiators running Windows® 2000, Windows® XP,or Windows® .NET operating systems. The connection recovery strategy ofan I_T nexus may be based on multiple Transmission Control Protocol(TCP) connections (Internet Engineering Task Force (IETF) Request forComments (RFC) 793, published September 1981). That is, packets fromiSCSI initiators running on Windows® operating systems are transmittedand/or received through multiple connections between an initiator and atarget. If multiple connections to the same target are establishedwithin one HBA, then a miniport driver may handle failover (i.e., whenone connection fails, routing packets to another connection) and loadbalancing (i.e., balancing the load among the HBA connections). However,there is a need in the art for failover and load balancing acrossseveral HBAs, each of which may have one or more connections to the sametarget.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings in which like reference numbers representcorresponding parts throughout:

FIG. 1A illustrates a computing environment in which certain embodimentsare implemented;

FIG. 1B illustrates a computing environment in which certain specificembodiments are implemented;

FIG. 2A illustrates, in a block diagram, a Windows® storage devicedrivers stack with an optional Class lower filter driver;

FIG. 2B illustrates, in a block diagram, a storage device drivers stackwith failover and load balancing capabilities that may be used in a SCSIenvironment in accordance with certain embodiments;

FIG. 3 illustrates, in a block diagram, an example of configuration ofan initiator with failover and load balancing capabilities in accordancewith certain embodiments;

FIGS. 4A and 4B illustrate operations for secondary storage device stackhiding in accordance with certain embodiments;

FIGS. 5A, 5B, and 5C illustrate operations for a notification mechanismin accordance with certain embodiments; and

FIGS. 6A and 6B illustrate operations for load balancing in accordancewith certain embodiments.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the following description, reference is made to the accompanyingdrawings which form a part hereof and which illustrate severalembodiments. It is understood that other embodiments may be utilized andstructural and operational changes may be made without departing fromthe scope of embodiments.

FIG. 1A illustrates a computing environment in which embodiments may beimplemented. A computer 102 acts as an initiator, while data storage 140acts as a target to form an I_T nexus. Computer 102 includes one or morecentral processing units (CPUs) 104, a volatile memory 106, non-volatilestorage 108 (e.g., magnetic disk drives, optical disk drives, a tapedrive, etc.), operating system 110 (e.g., Windows® 2000, Windows® XP, orWindows® .NET), and one or more network adapters 128. In certainembodiments, each network adapter is a Host Bus Adapter (HBA). A filterdriver 112, a miniport driver 114, and an application program 124further executes in memory 106.

The computer 102 may comprise a computing device known in the art, suchas a mainframe, server, personal computer, workstation, laptop, handheldcomputer, etc. Any CPU 104 and operating system 110 may be used.Programs and data in memory 106 may be swapped into storage 108 as partof memory management operations.

The data storage 140 includes one or more logical units (i.e., “n”logical units, where “n” may be any positive integer value, which incertain embodiments, is less than 128). Merely for ease ofunderstanding, logical unit 0, logical unit 1, and logical unit “n” areillustrated. Each logical unit may be described as a separate storagedevice. Additionally, a logical unit number (LUN) is associated witheach logical device. In certain embodiments, an HBA team is organizedbased on the target and LUN (i.e., each HBA that can route data to aparticular LUN of a target is grouped into one HBA team), and one HBAmay belong to different HBA teams.

Each network adapter 128 includes various components implemented in thehardware of the network adapter 128. Each network adapter 128 is capableof transmitting and receiving packets of data over network 176, whichmay comprise a Local Area Network (LAN), the Internet, a Wide AreaNetwork (WAN), Storage Area Network (SAN), WiFi (Institute of Electricaland Electronics Engineers (IEEE) 802.11b, published Sep. 16, 1999),Wireless LAN (IEEE 802.11b, published Sep. 16, 1999), etc.

Storage drivers 120 execute in memory 106 and include network adapter128 specific commands to communicate with each network adapter 128 andinterface between the operating system 110 and each network adapter 128.A network adapter 128 and storage driver 120 implement logic to processiSCSI packets, where a SCSI command is wrapped in the iSCSI packet, theiSCSI packet is wrapped in a TCP packet. The transport protocol layerunpacks the payload from the received Transmission Control Protocol(TCP) (Internet Engineering Task Force (IETF) Request for Comments (RFC)793, published September 1981) packet and transfers the data to thestorage driver 120 to return to, for example the application program124. Further, an application program 124 transmitting data transmits thedata to the storage driver 120, which then sends the data to thetransport protocol layer to package in a TCP/IP packet beforetransmitting over the network 176.

A bus controller 134 enables each network adapter 128 to communicate ona computer bus 160, which may comprise any bus interface known in theart, such as a Peripheral Component Interconnect (PCI) bus, PCI expressbus, Industry Standard Architecture (ISA), Extended ISA, MicroChannelArchitecture (MCA), etc. The network adapter 128 includes a physicalcommunication layer 132 for implementing Media Access Control (MAC)functionality to send and receive network packets to and from remotedata storages over a network 176. In certain embodiments, the networkadapter 128 may implement the Ethernet protocol (IEEE std. 802.3,published Mar. 8, 2002), Fibre Channel (IETF RFC 3643, publishedDecember 2003), or any other network communication protocol known in theart.

The storage 108 may comprise an internal storage device or an attachedor network accessible storage. Programs in the storage 108 are loadedinto the memory 106 and executed by the CPU 104. An input device 150 isused to provide user input to the CPU 104, and may include a keyboard,mouse, pen-stylus, microphone, touch sensitive display screen, or anyother activation or input mechanism known in the art. An output device152 is capable of rendering information transferred from the CPU 104, orother component, such as a display monitor, printer, storage, etc.

In certain embodiments, in addition to the storage drivers 120, thecomputer 102 may include other drivers.

The network adapter 128 may include additional hardware logic to performadditional operations to process received packets from the computer 102or the network 176. Further, the network adapter 128 may implement atransport layer offload engine (TOE) to implement the transport protocollayer in the network adapter as opposed to the computer storage driver120 to further reduce computer 102 processing burdens. Alternatively,the transport layer may be implemented in the storage driver or otherdrivers 120 (for example, provided by an operating system).

Various structures and/or buffers (not shown) may reside in memory 106or may be located in a storage unit separate from the memory 106 incertain embodiments.

FIG. 1B illustrates a computing environment in which certain specificembodiments are implemented. In FIG. 1B, computer 102 includes storagedrivers 120 interacting with Host Bus Adapters (HBAs) 128 a, 128 b, and128 c. Each HBA 128 a, 128 b, and 128 c may be described as a networkadapter 128 (FIG. 1A). The computer 102 and HBAs 128 a, 128 b, and 128 cmay be described as initiator, while the data storage 140 may bedescribed as a target. The data storage 140 illustrates Logical UnitNumbers (LUNs) that represent logical units.

FIG. 2A illustrates, in a block diagram, a Windows® storage devicedrivers stack 200 with optional Class lower filter driver. The storagedevice driver stack 200 includes an upper layer protocol (ULP) 210,which may send packets to and receive packets from a storage classdriver 212. The storage class driver 212 may send packets to and receivepackets from a class lower filter driver 214. The class lower filterdriver 214 is optional in certain embodiments. The class lower filterdriver 214 may send packets to and receive packets from a port driver216. The port driver 216 communicates with a miniport driver 218. Theminiport driver 218 is able to communicate with the class lower filterdriver 214 via callback interfaces which are provided by embodiments.

Embodiments provide a special filter driver based on the class lowerfilter driver 214 above the port driver 216 to provide for failover andload balance between cross-HBA connections. The filter driver handlesHBA context-switching and path control. The filter driver also providespacket distribution. In particular, the filter driver sniffs SCSIRequest Blocks (SRBs) packets included in Input/Output Request Packets(IRPs) between the storage class driver 212 and port driver 216. Incertain embodiments, the filter driver is implemented as a lower-levelclass filter driver. The filter driver is notified as soon as a storagedevice instance is created, and then, the filter driver attaches itselfto the storage driver stack 200 under the class lower filter driver 214.

FIG. 2B illustrates, in a block diagram, a storage device drivers stack250 with failover and load balancing capabilities that may be used in aSCSI environment in accordance with certain embodiments. The storagedevice drivers stack 250 may be used with a Windows® 2000, Windows® XPor Windows® .NET operating system. The storage device drivers stack 250includes an upper layer protocol (ULP) 260, which may send IRPs to andreceive IRPs from a SCSI disk class driver 262. The SCSI disk classdriver 262 may send SRBs/IRPs to and receive SRB/IRP from a lower levelclass filter driver 264. The lower level class filter driver 264 maysend SRBs/IRPs to and receive SRBs/IRPs from a SCSI port driver 266. TheSCSI port driver 266 communicates with a SCSI miniport driver 268. TheSCSI miniport driver 268 is able to communicate with the lower levelclass filter driver 264 via callback interfaces.

FIG. 3 illustrates, in a block diagram, an example of configuration ofan initiator with failover and load balancing capabilities in accordancewith certain embodiments. In FIG. 3, storage class drivers communicatewith a filter driver, which communicates with a port/miniport driver.For example, a storage class driver communicates with a filter driverusing storage class driver1 device object 310 and filter driver1 deviceobject 312, the filter driver communicates with a port/miniport driverusing filter driver1 device object 312 and port/miniport driver deviceobject 316, 314. A miniport driver communicates with an HBA via portdriver exported routines. Each HBA has communication paths to one ormore targets. For example, HBA1 318 has communication paths to target1320 and target2 340. HBA2 338 has communication paths to target1 320 andtarget2 340. HBA3 358 has communication paths to target2 340 and target3360. Embodiments provide failover and load balancing across HBAs 318,338, and 358, some of which have connections to a same target. Incertain embodiments, the proposed failover and load balancing approachis based on HBA teaming, built on an iSCSI portal group concept.

Again, in certain embodiments, an HBA team is organized based on thetarget and LUN (i.e., each HBA that can route data to a particular LUNof a target is grouped into one HBA team), and one HBA may belong todifferent HBA teams. For example, data may pass through data pathsincluding filter driver1 device object 312, filter driver4 device object332, and filter driver5 device object 352 to a same LUN (not shown)within target2 340. Each of these data paths passes through a differentHBA (HBA1 318, HBA2 338, and HBA3 358, respectively), and so HBA1 318,HBA2 338, and HBA3 358 are in one HBA team. That is, for each HBA in anHBA team, data routed to a LUN within target 2 340 may flow through anyHBA in the HBA team (for failover) or may flow through each of the HBAsin the HBA team simultaneously (for load balancing). As another example,an HBA team is also formed by HBA1 318 and HBA2 338, becausecorresponding data paths pass through HBA1 318 and HBA2 338 to a LUN(not shown) in target1 320.

Embodiments provide new callback interfaces for implementing failoverand load balancing capabilities in a filter driver.

The failover techniques provide high availability of communication pathsto a target when a first HBA or data path thought the first HBA fails(i.e., packets are routed to a second HBA that is connected to the sametarget). For failover, embodiments provide secondary storage devicestack hiding and a notification mechanism.

FIGS. 4A and 4B illustrate operations for secondary storage device stackhiding in accordance with certain embodiments. Control begins at block400 with a storage device stack being built for a logical unit. In block402, it is determined whether this is the first storage device stack forthis logical unit. If so, processing continues to block 404, otherwise,processing continues to block 404. That is, when there are several HBAsconnected to the same target, a storage device stack is created for eachSCSI LUN of the target for each of the HBAs to enable the filter driverto handle and redirect SRBs for each HBA. If the file system were tomount on each of the storage device stacks being built for the sametarget, this can lead to synchronization problems due to multipleaccesses to the same storage device instance. Therefore, the firststorage device stack built for each LUN becomes a “primary” storagedevice stack. After that, all other storage device stacks built for theLUN are treated as “secondary” storage device stacks. So, in block 404,the storage device stack is designated as a primary storage devicestack. In block 406, the storage device stack is designated as asecondary storage device stack.

For example, the storage device stack of storage class driver1 deviceobject 310, filter driver1 device object 312, port/miniport driverdevice object 314, 316 is designated a primary storage device stack inthis example. The storage device stack of storage class driver 1 adevice object 330, filter driver4 device object 332, port/miniportdriver device object 334, 336 is designated a secondary storage devicestack in this example. The storage device stack of storage class driver1 a device object 350, filter driver5 device object 352, port/miniportdriver device object 354, 356 is designated a secondary storage devicestack in this example. The filter driver enables file system mounting onone, primary storage device stack (e.g., storage device stack 310, 312,314, and 316) and prevents file system mounting on the other, secondarystorage device stacks (e.g., storage device stack 330, 332, 334, and 336and storage device stack 350, 352, 354, and 356). Likewise, the storagedevice stack starting with storage class driver2 device object is aprimary storage device stack, while the storage device stack startingwith storage class driver 2 a device object is a secondary storagedevice stack. Because of secondary storage device stack hiding, data isrouted through the primary storage device stacks and not through thesecondary storage device stacks.

In FIG. 4B, control begins at block 420 with a packet being completedfrom a secondary storage device stack with success status. In block 422,the filter driver changes the success status to an error status. Inblock 424, the filter driver sets the sense key value to not ready. Inblock 426, the filter driver sets the sense code to indicate that nomedia is in the storage device. Thus, in certain embodiments, to preventthe file system mounting on the secondary storage device stacks, thefilter driver flips the status of SRBs completed from the secondarystorage device stacks with success status to error status (e.g.,SRB_STATUS_ERROR), sets a sense key value to SCSI_SENSE_NOT_READY andsets an additional sense code to SCSI_ADSENSE_NO_MEDIA_IN_DEVICE.

FIGS. 5A, 5B, and 5C illustrate operations for a notification mechanismin accordance with certain embodiments. The filter driver and miniportdriver implement a protocol for interaction with each other.

FIG. 5A illustrates operations for failover processing implemented in aminiport driver in accordance with certain embodiments. In FIG. 5A,control begins at block 500 with receipt of a packet for a particularHBA data path at the miniport driver. The term “HBA data path” may bedescribed as a data path from a miniport via an HBA to a target. Onetype of packet may be an SRB. In block 502, if the HBA data path hasfailed, the processing continues to block 504, otherwise, processingcontinues to block 508.

In block 504, the miniport driver uses the notification callback methodto notify the filter driver that the HBA data path has failed.Optionally, the miniport driver provides a new HBA data path identifierto the filter driver, and the filter driver redirects packets to thisnew HBA data path. For example, for the HBA team formed by HBA1 318,HBA2 338, and HBA3 358, if HBA1 318 fails, the miniport may specify anew HBA data path including either HBA2 338 or HBA3 358. In certainembodiments, a pointer to the notification callback method and a pointerto the filter device extension for a current HBA data path may be sentto the miniport driver via an I/O control (IOCTL) in an add devicemethod of the filter driver. In certain embodiments, when a HBA datapath fails, the miniport driver notifies the filter driver of the HBAdata path fail by calling the notification callback method with a statusparameter and with a pointer parameter, where the pointer points to thedevice extension of the filter driver, corresponding to the currentpath.

The miniport driver does not complete packets with error status as thismay cause the port driver to freeze an SRB queue or initiate a busreset. Instead, in block 506, the miniport driver completes the pending(i.e., outstanding) and newly received packets for the failed HBA datapath with a success status. In block 508, since the HBA data path hasnot failed, the miniport driver sends the packet to the target via theHBA data path.

For example, if a SRB is received at miniport 316 for routing to HBA1318, and if HBA1 318 has failed, then the miniport driver 316 completesall pending SRBs for HBA1 318 as part of the protocol to notify thefilter driver 312 to redirect the SRBs to another HBA. For instance, thefilter driver 312 may redirect the SRBs to HBA2 338 or HBA3 358.

FIG. 5B illustrates operations implemented in a filter driver forfailover processing in accordance with certain embodiments. Controlbegins at block 510 with the filter driver receiving a HBA data pathfailure notification. In block 512, if a new HBA data path identifier isspecified by the miniport driver, processing continues to block 514,otherwise, processing continues to block 518. In block 514, the filterdriver changes the status of each packet being completed from the failedpath from success status to busy status. This change in status causesthe class driver to reissue the packets. When the packets are reissued,the filter driver treats them as new requests and, if possible,redirects them to a new path.

In block 516, the filter driver sends packets missed by the class driverto the specified HBA data path. In block 518, since a new pathidentifier is not specified, then the filter driver selects a new path.In certain embodiments, if there is just one path in an HBA team, thefilter driver continues to send new packets to the failed HBA data path(e.g., working in PATH_THROUGH mode).

FIG. 5C illustrates operations implemented in a miniport driver when anHBA is restored in accordance with certain embodiments. Control beginsat block 520 with a HBA data path being restored (e.g., an HBA isbrought online or an HBA or data path through this HBA that hadpreviously failed is restored). When a HBA data path has restored, theminiport driver notifies the filter driver by calling the notificationcallback method (block 522). In certain embodiments, the miniport drivernotifies the filter driver of the HBA data path restoration by callingthe notification callback method with a status parameter and with apointer parameter, where the pointer points to the device extension ofthe filter driver, corresponding to the current path. The miniportdriver may also pass the filter driver a new path identifier to whichthe filter driver should redirect new packets. In block 524, if a newHBA data path is specified, processing continues to block 526,otherwise, processing continues to block 528.

After the restore notification, if a new HBA data path is specified, thefilter driver sends the new packets to the new HBA data path (block526). If no new HBA data path is specified, the filter driver continuesto send the packets on the current active path.

In additional to failover processing, embodiments provide a filterdriver for balancing of I/O workload across multiple HBA data pathsspanning multiple HBAs. Embodiments provide static load balancing anddynamic load balancing.

FIGS. 6A and 6B illustrate operations for load balancing in accordancewith certain embodiments. For load balancing, each HBA data path in anHBA team has an associated value, referred to as a load balancing sharethat represents the percentage of a total I/O workload that the givenHBA data path is able to handle.

FIG. 6A illustrates operations for static load balancing in accordancewith certain embodiments. Control begins at block 600 with receipt of adata packet to be transmitted at the filter driver. In block 602, thefilter driver determines the load balancing share associated with eachHBA data path in the HBA team. For static load balancing, the loadbalancing shares may be specified manually and stored, for example, in aWindows® registry. The miniport driver retrieves the load balancingshare values and forwards these to the filter driver via thenotification callback method. On receiving the retrieved load balancingshare values, the filter driver updates the load balancing shares withnew values.

In block 604, the filter driver determines the moving mean data length(MDL) of the transmitted packets for each HBA data path (e.g., SCSItransfer length of the packets). In certain embodiments, load balancingmay be based on actual data length of transmitted packets, rather thanon a number of packets. In block 606, the filter driver determines adata quota for each HBA data path. In certain embodiments, the dataquota for a HBA data path is the MDL for the HBA data path multiplied bya ratio of the load balancing share for the HBA data path and a minimalvalue of a load balancing share in the HBA team (i.e., dataquota=MDL*(load balancing share/minimal load balancing share in team)).

In certain embodiments, MDL is recalculated for each packet or group ofpackets, while data quotas are recalculated periodically (e.g., after acertain number of packets are transferred). The periodic intervals maybe determined by a product of the number of HBA data paths in the HBAteam and a tunable load balancing frequency update factor. The loadbalancing frequency update factor allows tuning of load balancing andincreases performance. The load balancing frequency update factor may beset, for example, by a system administrator. The higher the frequency ofupdating of data quotas, the less difference between specified andactual load balancing shares. Also, more frequent updates may take upmore processor time.

In block 608, the filter driver determines a maximum number of commandsfor a target logical unit. In block 610, the filter driver selects a HBAdata path on which to send the packet using a round robin technique inwhich packets are sent along one HBA data path until a data quota isreached or a maximum of commands per the target logical unit is reached.

That is, for static load balancing, a round-robin technique may be used.In certain embodiments, valid HBA data paths for a current HBA team arecollected in a double-linked list for the round-robin operation. Then,HBA data paths are switched during the load balancing operation usingthis list. Otherwise, the packet flow switches to the next HBA teammember. That is, in certain embodiments, sending of packets for a givenpath continues until the amount of data transferred reaches thepreviously calculated data quota for this HBA data path or a maximumnumber of SCSI commands per a target LUN is reached.

For static load balancing, the actual distribution of packets among theHBA data paths may differ from a specified distribution (i.e., loadbalancing shares specified by, for example, a system administrator). Theless difference between the actual and specified distributions, thehigher the quality of the static load balancing. The specified loadbalancing share values affect the performance of static load balancing.

FIG. 6B illustrates operations for dynamic load balancing in accordancewith certain embodiments. Dynamic load balancing avoids congestion on asingle HBA data path as long as there is available bandwidth on otherpaths by dynamically adjusting I/O workload among paths. Thus, dynamicload balancing attempts to enable more efficient use of astorage/network available bandwidth.

Control begins at block 620 with the filter driver receiving a datapacket. In block 622, the filter driver determines a data transfer speedfor each HBA data path in the HBA team. In certain embodiments, datatransfer speed is calculated for each HBA data path as a ratio of totaldata transferred and total time spent on transferring data. An updatingroutine determines how frequently the transfer speeds are to be updated.A tunable parameter for dynamic load balancing is a transfer speedupdate frequency factor, which defines how often the updating routine isto be invoked. The transfer speed update frequency factor may be tunedbased on the specific behavior of the delivery subsystem.

In block 624, the filter driver updates the load balancing share foreach HBA data path. Load balancing shares for each path in the HBA teammay be updated proportionally to their data transfer speed (i.e., datatransfer speed for the selected HBA data path divided by HBA team's datatransfer speed). In block 626, the filter driver selects a HBA data pathon which to send the packet based on the load balancing shares.

While working in failover and load balancing mode, HBA failures disableone or more HBA team members. With embodiments, the remaining HBA teammembers continue functioning, maintaining the same ratio between theload balancing shares specified.

Thus, embodiments provide a combination of high availability and staticand dynamic load balancing. A software module that implements thesolution is relatively small and poses minimal overhead on the system.Embodiments provide the ability to quickly and easily turn on and offthe functionality provided by embodiments of the solution byinsertion/removal of the filter driver to/from the device stack.Embodiments are compatible across various platforms (e.g., Windows®platforms, either 32 bit or 64 bit). Also, embodiments are applicable toany SCSI and/or iSCSI based SAN and/or Network Attached Storage (NAS)system. Moreover, embodiments for failover and load balancing supportmultiple (two or more) HBAs.

Additional Embodiments Details

The described techniques for failover and load balancing may beimplemented as a method, apparatus or article of manufacture usingstandard programming and/or engineering techniques to produce software,firmware, hardware, or any combination thereof. The term “article ofmanufacture” as used herein refers to code or logic implemented inhardware logic (e.g., an integrated circuit chip, Programmable GateArray (PGA), Application Specific Integrated Circuit (ASIC), etc.) or acomputer readable medium, such as magnetic storage medium (e.g., harddisk drives, floppy disks, tape, etc.), optical storage (CD-ROMs,optical disks, etc.), volatile and non-volatile memory devices (e.g.,EEPROMs, ROMs, PROMs, RAMs, DRAMs, SRAMs, firmware, programmable logic,etc.). Code in the computer readable medium is accessed and executed bya processor. The code in which preferred embodiments are implemented mayfurther be accessible through a transmission media or from a file serverover a network. In such cases, the article of manufacture in which thecode is implemented may comprise a transmission media, such as a networktransmission line, wireless transmission media, signals propagatingthrough space, radio waves, infrared signals, etc. Thus, the “article ofmanufacture” may comprise the medium in which the code is embodied.Additionally, the article of manufacture may comprise a combination ofhardware and software components in which the code is embodied,processed, and executed. Of course, those skilled in the art recognizethat many modifications may be made to this configuration withoutdeparting from the scope of embodiments, and that the article ofmanufacture may comprise any information bearing medium known in theart.

In the described embodiments, certain logic was implemented in a driver.In alternative embodiments, the logic implemented in the driver and/ornetwork adapter may be implemented all or in part in network hardware.

In certain embodiments, the network adapter may be implemented as a PCIcard. In alternative embodiments, the network adapter may compriseintegrated circuit components mounted on the computer 102 motherboard.

In certain embodiments, the network adapter may be configured totransmit data across a cable connected to a port on the network adapter.In alternative embodiments, the network adapter embodiments may beconfigured to transmit data over a wireless network or connection, suchas wireless LAN.

The illustrated logic of FIGS. 4A, 4B, 5A, 5B, 5C, 6A, and 6C showcertain events occurring in a certain order. In alternative embodiments,certain operations may be performed in a different order, modified orremoved. Moreover, operations may be added to the above described logicand still conform to the described embodiments. Further, operationsdescribed herein may occur sequentially or certain operations may beprocessed in parallel. Yet further, operations may be performed by asingle processing unit or by distributed processing units.

The foregoing description of various embodiments has been presented forthe purposes of illustration and description. It is not intended to beexhaustive or to limit the embodiments to the precise forms disclosed.Many modifications and variations are possible in light of the aboveteaching. It is intended that the scope of the embodiments be limitednot by this detailed description, but rather by the claims appendedhereto. The above specification, examples and data provide a completedescription of the manufacture and use of the composition of theembodiments. Since many embodiments can be made without departing fromthe spirit and scope of the embodiments, the embodiments reside in theclaims hereinafter appended.

1. A method in a computer system for failover when at least one of afirst network adapter and a data path through the first network adapterfails, wherein the computer system includes a filter driver, and whereinthe first network adapter is connected to a second network adapter,comprising: receiving, with the filter driver, a path fail notificationthat at least one of the first network adapter and the data path throughthe first network adapter has failed; rerouting, with the filter driver,packets directed to the first network adapter to the second networkadapter; and changing, with the filter driver, a success status of eachpacket that had been directed to the first network adapter before thepath fail notification was received to a busy status, wherein the changein status causes each packet to be reissued.
 2. The method of claim 1,further comprising: determining, with the filter driver, a new data pathincluding the second network adapter.
 3. The method of claim 1, furthercomprising: receiving, with the filter driver, a notification that thefirst network adapter is restored; and determining, with the filterdriver, a data path for new data packets based on whether thenotification specified a new data path.
 4. The method of claim 1,further comprising: designating, with the filter driver, a first storagedevice stack as a primary storage device stack in response to buildingthe first storage device stack for a logical unit; and designating, withthe filter driver, a subsequent storage device stack as a secondarystorage device stack in response to building the subsequent storagedevice stack for the logical unit.
 5. The method of claim 4, furthercomprising: preventing, with the filter driver, file system mounting onthe secondary storage device stack.
 6. A system coupled to a network anddata storage, comprising: a host computer; a storage controller managingInput/Output (I/O) access to the data storage, wherein the storagecontroller is coupled to the host computer; a first network adapter asecond network adapter; and a filter driver at the host computer,wherein the filter driver is capable of receiving a path failnotification that at least one of the first network adapter and a datapath through the first network adapter has failed, rerouting packetsdirected to the first network adapter to the second network adapter;changing a success status of each packet that had been directed to thefirst network adapter before the path fail notification was received toa busy status, wherein the change in status causes each packet to bereissued.
 7. The system of claim 6, wherein the filter driver is furthercapable of: determining a new data path including the second networkadapter.
 8. The system of claim 6, wherein the filter driver is furthercapable of: receiving a notification that the first network adapter isrestored; and determining a data path for new data packets based onwhether the notification specified a new data path.
 9. The system ofclaim 6, wherein the filter driver is further capable of: designating afirst storage device stack as a primary storage device stack in responseto building the first storage device stack for a logical unit; anddesignating a subsequent storage device stack as a secondary storagedevice stack in response to building the subsequent storage device stackfor the logical unit.
 10. The system of claim 9, wherein the filterdriver is further capable of: preventing file system mounting on thesecondary storage device stack.
 11. An article of manufacture comprisinga storage medium having stored therein instructions that when executedby a computing device results in the following: at a filter driver,receiving a path fail notification that at least one of a first networkadapter and a data path through the first network adapter has failed;rerouting packets directed to the first network adapter to the secondnetwork adapter; and changing, with the filter driver, a success statusof each packet that had been directed to the first network adapterbefore the path fail notification was received to a busy status, whereinthe change in status causes each packet to be reissued for processingagain by the filter driver.
 12. The article of manufacture of claim 11,the instructions when executed further result in the following:determining a new data path including the second network adapter. 13.The article of manufacture of claim 11, the instructions when executedfurther result in the following: receiving a notification that the firstnetwork adapter is restored; and determining a data path for new datapackets based on whether the notification specified a new data path. 14.The article of manufacture of claim 11, the instructions when executedfurther result in the following: designating a first storage devicestack as a primary storage device stack in response to building thefirst storage device stack for a logical unit; and designating asubsequent storage device stack as a secondary storage device stack inresponse to building the subsequent storage device stack for the logicalunit.
 15. The article of manufacture of claim 14, the instructions whenexecuted further result in the following: preventing file systemmounting on the secondary storage device stack.